robot_localization perform worst just adding magnetometer to imu_filter_madgwick

edit

Hi, I'm trying to find some robot_localization issue on my unmanned surface vessel. So I've started with the simplest case: integrating just the IMU x and y acceleration on a table (I'm mean, a static test) I'm using an ICM20602 and published data @100Hz using rosserial to raspberry pi 3b+. In the Pi I have a robot_localization ekf node, some static tf and imu_filter_madgwick. imu_filter output is on /chori/imu/data topic. I've recorded two bagfile, one setting (param name="~use_mag" value="true") and another with param name="~use_mag" value="false"

In the first case, position output from RL increased very fast. In the second case, position output increase slowly, as I expected. I can't find any difference on linear acceleration output from imu_filter with and without "use_mag" parameter equal to "true" or "false".

launch, config and bag files: https://drive.google.com/file/d/1EUJ7...

EDIT: I'm trying to get position/velocity of my unmanned surface vessel. I have RTK GPS position and velocity in order to correct unbounded errors from the IMU. But on my field test I've noticed some extrange behavior between 2 GPS measurements. That is when the filter is using the IMU. So, as I said, I decide to make some static test using just the IMU (first) to see if I can find some issue. In this test I found that fusing just accelorometer data from imu_filter with and without magnetometer enabled make RL EKF perform really bad. I know that I will have unbounded position error, but with magnetometer enabled the error grows very fast compared with magnetometer disabled. My question is why?

EDIT2: Just to clarify a little the test. I have IMU data (raw accelerometer, gyroscope and magnetometer) coming in to two imu_filter_madgwick instances. One of them have use_mag=true ans the other =false. Each output is used for two instance of RL ekf filter. Each one is configured to just fuse acceleration data, and working on 2D mode: imu0: chori/imu/data_mag imu0_config: [false, false, false, # x, y, z, false, false, false, # roll, pitch, yaw false, false, false, # vx, vy, vz false, false, false, # vroll, vpitch, vyaw true, true, false] # ax, ay, az I expect that velocity and position output growth unbounded. But as I'm making an static test I expect the output increase "slowly".

This is the X acceleration output of each imu_filter. As you can see both of them are equal. The same is for Y and Z axis.

Then thing is that RL output increase faster on imu_filter instance with use_mag=true:

And as you can see, in 10 second it accumulate 2mts of error, wich is a lot compared with a couple of centimeter on the RL with acceleration data coming from imu_filter instance with use_mag=false.

Thank